The invention relates to water-dilutable, hydroxy-functional polyurethanes containing amide structural units, to a process for preparing them, to aqueous coating compositions prepared from them, and to their use for coating substrates.
For years the efforts at weight saving in the passenger car sector have gone hand in hand with increased use of plastic, in the interior as well. Because of aesthetic and technical requirements, plastics components in the car are typically coated, in order to protect the plastic against external influences, such as sunlight and chemical, thermal and mechanical exposure, in order to obtain certain shades and colour effects, in order to mask defects in the plastic surface or in order to give the plastic surface a pleasant feel (tactility). In order to enhance the tactile properties of plastics components in the car interior, use has been made increasingly in recent years of what are called soft feel coating materials. “Soft feel effect” for the purposes of the present invention denotes a particular tactual sensation (tactility) of the coated surface. This tactility can be described using terms such as velvety, soft, rubber-like or warm, whereas, for example, the surface of a painted car body or else an unpainted polymeric sheet or plexiglass, or a similar plate or plexiglass coated with a customary clearcoat or topcoat material, feels cold and smooth.
Aqueous soft feel coating materials based on the polyurethane chemistry are disclosed by way of example in EP-A 0 669 352. As well as an excellent soft feel effect, these coating materials also produce coatings of high stability and protective effect for the plastics substrate.
In the intervening period the requirements imposed on soft feel coating materials for the automotive interior sector, particularly in respect of resistance to creams used for skin protection and skincare (e.g. sun cream or sun lotion), have risen to such an extent that these requirements can be met not at all, or only with detractions in terms of the soft feel effect, by the state-of-the-art coating materials.
There continues to be a need for aqueous coating compositions which have good resistance properties, particularly towards creams used for skin protection and skincare, while at the same time having a pronounced soft feel effect.
Surprisingly it has now been found that water-dilutable, hydroxy-functional polyurethanes comprising amide structural units are suitable for producing coating materials featuring excellent resistance towards, for example, creams used for skin protection and skincare, such as sun cream or sun lotion, and having at the same time an outstanding soft feel effect.
U.S. Pat. No. 5,780,559 discloses film-forming polyurethanes which contain terminal amide groups and can be crosslinked using melamine resins. The acid resistance and hardness of the coatings are high. However, the polyurethanes disclosed therein are not suitable for use in aqueous systems. Furthermore, the film-forming polymers described are not suitable for application in the automotive interior sector, since the temperatures needed for this crosslinking cannot be employed for the plastics materials that are typically used in the automotive interior sector.
US-A 2002/0068789 discloses aqueous dispersions of polyurethanes containing amide groups, but again without the structures according to the invention. They are reacted with crosslinking agents that are reactive towards amide groups. Thermally curable one-component systems are obtained which are used in particular in the passenger car sector as OEM coatings.
An object of the present invention was therefore to provide a suitable polyurethane component which, in conjunction with isocyanate crosslinkers, produces coating compositions which possess a soft feel effect and are at the same time particularly resistant to skin protection and skincare creams, especially sun protection creams.
This object is achieved through the water-dilutable polyurethanes of the invention.